func ByFiles

Description

ByFiles returns a filter that selects objects that are defined in
or contain any of the listed files. It panics if any file path is
empty, or if the file path has not been cleaned (i.e., if file !=
path.Clean(file)).

If exact == true, then only the exact files are accepted (i.e. a directory
path will not include all files in that directory as it would normally).